  
.main {
  width: 370px;
  margin: 50px auto;
  font-size: 1.1em;
}

input, label, span {
  margin: 5px 0;
  font-size: 1em;
  padding-left: 5px;
}

#calc {
  width: 70px;
  margin-left: 63px;
}

span {
  color: red;
}

#width-validate,
#height-validate {
  color: red;
  margin-left: 63px;
  font-size: 0.8em;
}